Hemofiltration and dialysis, including hemodialysis and peritoneal dialysis, are different types of treatment for patients that suffer from kidney failure. In hemodialysis, the patient's blood is utilized to remove waste, toxins and excess water from the patient. The patient is connected to a hemodialysis machine and the patient's blood is pumped through the machine. Catheters are inserted into the patient's veins and arteries to connect the blood flow to and from the hemodialysis machine. As blood passes through a dialyzer in the hemodialysis machine, the dialyzer removes the waste, toxins and excess water from the patient's blood and returns the blood to infuse back into the patient. In hemofiltration, toxins and excess water are also removed from the patient's blood. However, in hemofiltration, the patient is connected to the hemofiltration system—intermittently or continuously—and blood from the patient passes through a system with a hemofilter. In contrast to hemodialysis, no dialysate is used in hemofiltration and the movement of solvent and solutes across the membrane is governed by convection rather than diffusion, mimicking the microfiltration process of a normal kidney. It may be necessary to add an isotonic replacement fluid to the blood—before or after the hemofilter—to replace losses of fluid volume and electrolytes. In continuous hemofiltration between 0 and 2000 mL of water may be lost per hour. This means that a considerable volume of water may have to be replaced depending on the individual patient's need. In hemofiltration, the demand for replacement fluid can be as much as 3 to 4 liters per hour.
In contrast, a large amount of dialysate, for example about 120 liters, is used to dialyze the blood during a single hemodialysis therapy. The spent dialysate in then discarded. This means that a patient undergoing hemodialysis therapy three times weekly could be exposed to nearly 600 liters of purified water. By comparison, a healthy individual would intake around 2 liters per day or 14 liters per week. In addition, large amounts of purified water are used for peritoneal dialysis, such as 12 liters per day during continuous ambulatory peritoneal dialysis, CAPD, and up to 25 liters per night during automatical fluid replacement while the patient is sleeping (automated peritoneal dialysis, APD). Dialysis is a life saving treatment for end stage kidney disease patients. However, it requires large scale consumption of highly purified water for the preparation of replacement fluids as well as dialysate solutions.
In WO2010/146365 A1 it has been suggested to recover purified water lost during hemodialysis by the use of a liquid membrane system comprising vesicles having a bilayer into which biochannels such as aquaporin water channels have been incorporated and wherein the vesicles further comprise a stabilising oil phase. In order to accomplish this it was suggested to create a salt gradient and a counter-current mimicking the normal kidney function across said liquid membrane, which will then constitute the necessary driving force for a forward osmosis processes. Talaat (Saudi J Kidney Dis. Transpl., 21(4):748-749, 2010) later proposed to use forward osmosis for dialysis fluid regeneration where theoretically up to 50% of spent dialysis fluid water may be retrieved. However, due to limitations on draw solutes such as salts and glucose, Talaat concludes that a modified dialysis therapy prescription such as a prolonged daily therapy is necessary, and he further proposes to use a multilayer FO plate and frame module to be specifically built for testing the hypotheses.
Thus, various energy consuming processes for water purification are needed, e.g. activated carbon filtration, ion exchange, reverse osmosis, ultrafiltration and the like, to remove unwanted and even toxic substances of mineral and organic origin from the purified water.